Introduced by Senate President Pro Tem Kevin de León in late 2016, shortly after the election of President Donald Trump, SB 54 aims to prevent California police resources from being “commandeered” by the Trump administration as it ramps up deportations.

Ben Bergquam, a spokesman for the referendum campaign, said those efforts to “undermine” the federal government amount to “sedition.”“It’s lawless. It’s politicians protecting criminal illegals at the expense of law-abiding citizens,” he said. “It’s a slap in the face to American sovereignty and the citizens of our country.”

Proponents have until Jan. 3, 2018, to collect signatures from at least 365,880 registered voters. If they are successful, the referendum will appear on the November 2018 ballot, where voters will be asked whether or not to uphold SB 54. Bergquam said the campaign has no major funders yet, but it is reaching out to law enforcement groups that oppose the law.

Gov. Jerry Brown signed SB 54 earlier this month, capping months of intense negotiations and lobbying by immigrant rights’ advocates and law enforcement organizations. It is set to take effect at the start of 2018, though it would be placed on hold pending the outcome of the vote if the referendum qualifies for the ballot.

Supporters argue that “sanctuary” policies allow law enforcement officers to maintain crucial relationships with immigrant communities, while critics, including the California State Sheriffs’ Association and conservative lawmakers, contend that SB 54 endangers the public by protecting criminals.